This is a BIG win for Netflix, period. Because of the Wii's expanded audience however, Netflix is going to need to do a decent amount of marketing to be able to get the user numbers they want. Furthermore, I don't think that this userbase is the kind that cares all that much about HD, so that's another big plus as well.
I already have Netflix on my Tivo, but I'll definitely add it to my Wii as well